I have blogged about using JoyBidder Pro to monitor Buy It Now items price drop on eBay. Here is a simple guide to set up price alert and receive email when price changes.
Step 1: Add the items to JoyBidder. One of the many ways to do this to add the items using the item numbers.
Step 2: Select the items and right click the mouse button to bring up the popup menu, and enable the Price Alert.
Step 3: Open the settings dialog and make sure you enable email alerts
Step 4: Show the Price Alert column in the list, which displays up or down arrow if there is any price changes for the items.